The role of satellite cells in skeletal muscle hypertrophy with aging

项目摘要 随着年龄的增长，骨骼肌量的减少具有重要的临床意义，因为它与 发病率和死亡率，以及生活质量的明显恶化。还有一种更高的 对缺乏合成代谢物的细胞和分子机制的鉴定感兴趣 衰老肌肉对肥大刺激的反应。利用卫星细胞治疗骨骼肌块丢失 被认为是一种有前途的治疗策略，考虑到它们的干细胞特性和在后循环中的重要作用 出生时肌肉的生长和再生。我们的研究结果促使我们进行机械化的 分析卫星细胞的两个众所周知的功能；融合到肌纤维，为 肥厚性生长，以及卫星细胞扩张的其他功能后果 各种外源刺激，如运动，作为对卫星细胞丰度增加的反应 机械负荷远远超过与肌纤维大小增加相关的肌核增大。我们报道了 卫星细胞是骨骼肌最佳长期肥大生长所必需的，通过调节 细胞外基质。激活的卫星细胞通过胞外小泡抑制成纤维细胞胶原的产生 (Ev)交付miR-206，揭示了卫星细胞以前未被认识到的功能，除了提供 一种卫星细胞与肌肉内其他细胞交流的机制。我们现在已经有了活体 Pax7-TdT报告小鼠卫星细胞间通讯的单细胞(Sc)RNA-seq证据 卫星细胞与FAP/纤维化细胞和内皮细胞之间的通讯网络 肥厚性生长。目标1将检验老龄化对通信网络产生负面影响的假设 抑制细胞外基质的适当重塑，从而抑制肥大。我们还开发了 一种新的小鼠模型，允许我们同时耗尽卫星细胞和标记驻留的肌核，AIM 2将使用这一模型和单肌核(SMN)RNA-seq来表征年龄相关性的变化。 驻留的肌核转录组和识别在缺乏的情况下使短期肥大的机制 成年小鼠的卫星细胞，这种细胞在老年时就会消失。Aim 3将使用另一名新开发的记者 能够对卫星细胞核进行特定和稳定的标记以确定衰老如何改变的小鼠 卫星细胞衍生的肌核转录组对肥大刺激的反应。我们假设在 老化的肌肉，卫星细胞衍生的肌核改变了转录输出，而不促进 肥大反应，卫星细胞融合受损或有缺陷的卫星细胞可能为 影响常驻肌核转录活动，导致生长受损。定义聚变依赖 卫星细胞的独立作用和年龄相关的变化对肌肉适应性产生负面影响 将确定潜在的新目标，以促进骨骼肌在不活动、衰老和 面对肌肉衰弱的疾病。

Project Summary The loss of skeletal muscle mass with age is of clinical importance because it is associated with increased morbidity and mortality, as well as a marked deterioration in the quality of life. There is also a heightened interest in the identification of cellular and molecular mechanisms responsible for the lack of an anabolic response of aged muscle to hypertrophic stimuli. The use of satellite cells to treat loss of skeletal muscle mass is considered a promising therapeutic strategy given their stem cell characteristics and essential role in post- natal muscle growth and regeneration. The results of our studies have prompted us to perform mechanistic analyses of both of the well-known function of satellite cells; fusion to myofibers to provide additional nuclei for hypertrophic growth, to other functional consequences of satellite cell expansion that occurs in response to various exogenous stimuli such as exercise, as the increase in satellite cell abundance in response to mechanical overload far exceeds myonuclear accretion associated with increased myofiber size. We reported satellite cells were necessary for optimal long-term hypertrophic growth of skeletal muscle by regulating the extracellular matrix. Activated satellite cells repressed fibroblast collagen production via extracellular vesicle (EV) delivery of miR-206, revealing a previously unrecognized function of satellite cells, in addition to providing a mechanism through which satellite cells communicate with other cells within muscle. We now have in vivo single-cell (sc)RNA-seq evidence from Pax7-tdT reporter mice of a satellite cell intercellular communication network in which satellite cells communicate with FAPs/fibrogenic cells and endothelial cells during hypertrophic growth. Aim 1 will test the hypothesis that aging negatively impacts this communication network inhibiting proper remodeling of the extracellular matrix thereby inhibiting hypertrophy. We have also developed a novel mouse model that allows us to simultaneously deplete satellite cells and label resident myonuclei, Aim 2 will use this model and single-myonuclear (smn)RNA-seq to characterize age-dependent changes in the resident myonuclear transcriptome and identify mechanisms that enable short term hypertrophy in the absence of satellite cells in adult mice, which is lost in old age. Aim 3 will use an additional newly developed reporter mouse that enables specific and stable labeling of satellite cell nuclei to determine how aging alters the satellite cell-derived myonuclear transcriptome in response to a hypertrophic stimulus. We hypothesize that in aged muscle, satellite cell-derived myonuclei have altered transcriptional output that does not promote a hypertrophic response, and that impaired fusion of satellite cells or defective satellite cells may negatively impact resident myonuclear transcriptional activity contributing to impaired growth. Defining fusion-dependent and -independent roles of satellite cells and age-associated changes that negatively impact muscle adaptability will identify potential new targets to promote skeletal muscle growth in the face of inactivity, during aging and in the face of muscle wasting diseases.